Starting from the early 1990’s, the chemistry of polyvalent iodine organic compounds has experienced an explosive development. This surging interest in iodine compounds is mainly due to the very useful oxidizing properties of polyvalent organic iodine reagents, combined with their benign environmental character and commercial availability. Iodine(III) and iodine(V) derivatives are now routinely used in organic synthesis as reagents for various selective oxidative transformations of complex organic molecules. Several areas of hypervalent organoiodine chemistry have recently attracted especially active interest and research activity. These areas, in particular, include the synthetic applications of 2-iodoxybenzoic acid (IBX) and similar oxidizing reagents based on the iodine(V) derivatives, the development and synthetic use of polymer-supported and recyclable polyvalent iodine reagents, the catalytic applications of organoiodine compounds, and structural studies of complexes and supramolecular assemblies of polyvalent iodine compounds.

The chemistry of polyvalent iodine has previously been covered in four books1–4 and several comprehensive review papers.5–17 Numerous reviews on specific classes of polyvalent iodine compounds and their synthetic applications have recently been published.18–61 Most notable are the specialized reviews on [hydroxy(tosyloxy)iodo]benzene,41 the chemistry and synthetic applications of iodonium salts,29,36,38,42,43,46,47,54,55 the chemistry of iodonium ylides,56–58 the chemistry of iminoiodanes,28 hypervalent iodine fluorides,27 electrophilic perfluoroalkylations,44 perfluoroorgano hypervalent iodine compounds,61 the chemistry of benziodoxoles,24,45 polymer-supported hypervalent iodine reagents,30 hypervalent iodine-mediated ring contraction reactions,21 application of hypervalent iodine in the synthesis of heterocycles,25,40 application of hypervalent iodine in the oxidation of phenolic compounds,32,34,50–53,60 oxidation of carbonyl compounds with organohypervalent iodine reagents,37 application of hypervalent iodine in (hetero)biaryl coupling reactions,31 phosphorolytic reactivity of o-iodosylcarboxylates,33 coordination of hypervalent iodine,19 transition metal catalyzed reactions of hypervalent iodine compounds,18 radical reactions of hypervalent iodine,35,39 stereoselective reactions of hypervalent iodine electrophiles,48 catalytic applications of organoiodine compounds,20,49 and synthetic applications of pentavalent iodine reagents.22,23,26,59

The main purpose of the present review is to summarize the data that appeared in the literature following publication of our previous reviews in 1996 and 2002. In addition, a brief introductory discussion of the most important earlier works is provided in each section. The review is organized according to the classes of organic polyvalent iodine compounds with emphasis on their synthetic application. Literature coverage is through July 2008.

Chemistry of Polyvalent Iodine

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C–C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of...

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The recent groundbreaking developments in the application of diaryliodonium salts in cross-coupling reactions has brought this class of previously underdeveloped reagents to the forefront of organic chemistry. With the advent of novel, facile, and efficient synthetic routes to these compounds, many more applications can be foreseen. Herein we provide an overview of the historical and recent advances in the synthesis and applications of diaryliodonium salts.

Diaryliodonium Salts: A Journey from Obscurity to Fame

Review on Modern Advances of Chemical Methods for the Introduction of a Phosphonic Acid Group

Easy does it: The unique properties of benziodoxolone alkynyl periodinane 1 and gold catalysts have allowed the development of a high yielding, operationally simple (room temperature, no dry solvents or inert conditions, commercially available catalyst) reaction for the introduction of silylacetylenes on a large range of indole and pyrrole heterocycles with a wide range of functional groups (see scheme).

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Direct Alkynylation of Indole and Pyrrole Heterocycles

Reactions of vinylsilanes with lewis acid-activated iodosylbenzene: stereospecific syntheses of vinyliodonium tetrafluoroborates and their reactions as highly activated vinyl halides

Hydrogen fluoride-induced protiodetrimethylsilylation of trimethylsilylethynyl(phenyl)iodonium tetrafluoroborate (5), prepared from bis(trimethylsilyl)ethyne (4), affords ethynyl(phenyl)iodonium tetrafluoroborate (1), a reagent for α-ethynylation of β-dicarbonyl compounds under mild conditions.

Synthesis of ethynyl(phenyl)iodonium tetrafluoroborate. A new reagent for ethynylation of 1,3-dicarbonyl compounds

Hypervalent alkenyliodonium tetrafluoroborates. Evidence for generation of alkylidenecarbenes via base-induced .alpha.-elimination

Optically active 2-iodobinaphthyl (S)-(I) is transformed into iodo(III) derivative (S)-(III) by two ways.

Synthesis of chiral hypervalent organoiodinanes, iodo(III)binaphthyls, and evidence for pseudorotation on iodine

Reported for the first time are the generation of allenyliodinanes and their reductive iodonio-Claisen rearrangement Reaction of propargylsilanes, germanes, and stannanes with aryliodinanes in the presence of BF 3 -Et 2 O undergoes a reductive iodonio-Claisen rearrangement under mild conditions, yielding o-propargyliodoarenes in good yields The reductive ortho propargylation probably involves the intermediate formation of allenyl(aryl) iodinanes, which undergo [3,3]-sigmatropic rearrangement The lack of crossover products argues for the intramolecularity of the rearrangement When both ortho positions of aryliodinanes are occupied with alkyl substituents, the reductive iodonio-Claisen rearrangement affords meta substitution products This is the first to show that meta-Claisen rearrangement occurs preferentially even when a free para position is available The reductive ortho propargylation of iodinanes takes place under much milder conditions than the Claisen rearrangement The lower activation energy associated with the iodonio-Claisen rearrangement of allenyl(aryl) iodinanes can be interpreted in terms of the small bond energy of the breaking apical carbon-iodine (III) bond

Yoshikazu Takaoka

Papers

Reactions of vinylsilanes with lewis acid-activated iodosylbenzene: stereospecific syntheses of vinyliodonium tetrafluoroborates and their reactions as highly activated vinyl halides

Synthesis of ethynyl(phenyl)iodonium tetrafluoroborate. A new reagent for ethynylation of 1,3-dicarbonyl compounds

Hypervalent alkenyliodonium tetrafluoroborates. Evidence for generation of alkylidenecarbenes via base-induced .alpha.-elimination

Synthesis of chiral hypervalent organoiodinanes, iodo(III)binaphthyls, and evidence for pseudorotation on iodine

Generation of allenyliodinanes and their reductive iodonio-Claisen rearrangement